1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording where a magnetic recording medium is irradiated with near-field light to lower the coercivity of the magnetic recording medium for data writing.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head section including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the magnetic recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the magnetic recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the aforementioned problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a magnetic recording medium having high coercivity. When writing data, a write magnetic field and heat are applied almost simultaneously to the area of the magnetic recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the magnetic recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near field light from plasmons excited by irradiation with laser light. The laser light to be used for generating the near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near a medium facing surface of the slider.
U.S. Patent Application Publication No. 2010/0172220 A1 discloses a technology for coupling the light that propagates through the waveguide with the plasmon generator in surface plasmon mode via a buffer part, thereby exciting surface plasmons on the plasmon generator.
For a thermally-assisted magnetic recording head having the aforementioned waveguide and plasmon generator and a main pole for producing a write magnetic field, it is required that the main pole, a part of the core of the wave guide, and the plasmon generator be disposed in a very small region in the vicinity of the medium facing surface.
To meet the aforementioned requirement, the thermally-assisted magnetic recording head may be configured such that the plasmon generator and the core are disposed to align in the direction of travel of the magnetic recording medium, the core has an end face that faces toward the medium facing surface and that is located away from the medium facing surface, and the main pole is interposed between the end face of the core and the medium facing surface. In this configuration, the main pole may be in the shape of a rectangular solid. The main pole in this case has a rectangular front end face, which is the end face located in the medium facing surface.
To employ the aforementioned configuration, it is further required that the light propagating through the core be efficiently transformed into near-field light. To this end, it is preferred that the end face of the core facing toward the medium facing surface be as close to the medium facing surface as possible in order to allow the plasmon generator to excite surface plasmons at the nearest possible point to the medium facing surface. As the end face of the core is brought closer to the medium facing surface, the main pole decreases in length in a direction perpendicular to the medium facing surface. In this case, it is preferable to increase the width of the main pole in the track width direction to some extent so that the magnetic flux in the main pole will not be saturated at a small amount.
However, when the above configuration was employed and the width of the main pole in the track width direction was increased to some extent, the following problem was found to occur. A write magnetic field is a magnetic field leaking from the front end face of the main pole toward a recording medium. One of the known general properties of the main pole is that, when the main pole has an edge, the magnetic field leaking from the main pole tends to be strong in the vicinity of the edge. Therefore, when the width of the main pole in the track width direction is increased to some extent, magnetic fields that are generated from the vicinities of opposite track-widthwise ends of the front end face of the main pole are strong whereas a magnetic field that is generated from the vicinity of the track-widthwise center of the front end face of the main pole is weak. In this case, when an attempt is made to generate a write magnetic field of sufficient magnitude, the magnetic fields generated from the vicinities of opposite track-widthwise ends of the front end face of the main pole become excessively strong, and the excessively strong magnetic fields may cause a phenomenon that, when a signal is being written on a certain track, signals stored on one or more tracks adjacent to the track targeted for writing are erased or attenuated (this phenomenon will hereinafter be referred to as adjacent track erasure). To achieve higher recording densities, it is required to prevent the occurrence of adjacent track erasure.